Standardized Exercise Test - The subject pedals on a stationary bicycle for 20 minutes, while wearing the nose clip and mouthpiece to measure oxygen use. For the first 5 minutes, the subject pedals at a speed that elicits 50 percent of maximal effort (determined by the maximal exercise test); the next 10 minutes are at 70 percent of maximal effort; and the last 5 minutes are at 90 percent. Blood samples drawn before, during (at 15 and 20 minutes) and after exercise (at 30, 40 and 60 minutes) total less than 1/2 cup. Heart rate and heart activity are monitored during the test with an EKG, and temperature is measured before and at the end of the test.